Conventionally, there have been known various link devices applied to a robotic device used for assembly work, transport operation or the like (for example, Patent Documents 1 and 2). These link devices are generally set such that a movable range and applied load characteristics meet the work contents and purpose. A link structure described in Patent Document 1 is a closed-link structure composed of four links from a first link to a fourth link, the first link and the fourth link being rotatably connected to a base, and supports a hand (moving object) on the same axis as a connection axis of a second link with a third link.
A link structure described in Patent Document 2 is a closed-link structure composed of four links from a second link to a fifth link, the second link and a third link being rotatably connected to a fixed first link, and another end of a fourth link and another end of the fifth link can be connected to each other, so that a light work is carried out in a non-connected state, and an applied load greater than the light work can be received in a connected state.